The present invention relates to a ball valve assembly which can be made sufficiently large and robust to be installed in a pipeline, particularly an undersea oil pipeline. It may also be applied on a smaller scale.
A ball valve has a body with a through passage, and a rotatable ball member located in the body. The ball member has a through passage, and may be rotated between an "open" configuration. in which its through passage is in line with the through passage of the body, and a "closed" configuration in which the two through passages are no longer in register. The rotation of the ball member is generally effectable about a single axis transverse to the through passage of the body.
This general type of valve has been found to be the most suitable for use under arduous conditions such as in undersea oil pipelines, where large pressures are involved. In the known type of assembly, the body is closed by a bonnet which is secured by a multiplicity of bolts. It is periodically necessary to service the valve, particularly to repair or replace the seals. This requires a team of divers to descend to the seabed, and to remove the bonnet after undoing the bolts (which are likely to be severely corroded). Even after the bonnet has been removed, the operation is difficult. It is quite likely that the pipeline will have to be shut down for a period of two or three weeks. The costs involved are very substantial, e.g. of the order of 200,000 (Sterling).